This invention relates, in general, to a method and apparatus for unloading a pallet stacked with layers of similarly-shaped objects and, in particular, it relates to a method and apparatus for handling cases or cartons stacked on a pallet and for transferring them from the pallet to a conveyor. More particularly, the present invention relates to a method and apparatus for automatically successively transferring individual layers of cases containing empty bottles from a palletized stack of such cases with bottom flaps unglued to a conveyor system for transportation to bottle-filling lines. Still more particularly, the invention relates to a method and apparatus for unloading a pallet stacked with cases of bottles in such a manner that the unglued bottom flaps are placed on a conveyor so that the bottles may be removed by lifting each case leaving the bottles in an upright position (standing on their bottoms) ready to be transported to a filling machine.
It will be realized, of course, that the invention is applicable to depalletizing a stack of any parallelepiped-shaped objects, especially where similar orientation before and after being depalletized is a matter of concern.
In a bottling plant, empty bottles or jars are frequently received from a storage warehouse or glass plant packed in cardboard cartons or cases and stacked on pallets. Because the bottles must be removed from the cases before entering the automatic filling machine, the case flaps are ordinarily glued on one side only. Depending on the preferred practice in a given plant, the cases can be stacked on the pallet with their open, unglued sides either up or down.
To supply those bottling plants whose preferred practice is to stack the cases of empty bottles with the open, unglued flaps facing downward, empty cases are initially formed in an inverted position and their top flaps glued shut by machines which were designed specifically for this function. The cases are then carried by conveyor, riding on their glued top flaps (still inverted so that the bottom flaps project more or less vertically up) to the ends of the bottle production lines. At this point, the bottles are inserted into the cases through the open bottom, with the bottle finish or necks against the top glued flaps. The bottom flaps are then folded into closed position, but not glued, and the filled cases are then transported to palletizers, now riding on the folded unglued bottom flaps. The cases are then stacked on a pallet with the bottom flaps down and still unglued. If the cases are stacked on the pallets with their unglued flaps down and are transferred to the conveyor in that position, it is then merely necessary to lift off the cases to leave the bottles upright on the conveyor and ready for transfer to the filling machine.
Regardless of whether the cases are stacked with their open sides up or down, problems arise when an attempt is made to transfer the cases from the pallet to a moving conveyor by sliding the top layer of the stack horizontally onto the conveyor. These problems stem from the fact that the unglued flaps tend to interlock with the adjacent layer.
In small establishments handling a relatively low volume of cases and requiring little warehouse space for empty bottles, it is possible to insert a corrugated slip sheet between each layer of cases while the pallet is being loaded. When this is done, it is then very easy to slide one layer of cases off at a time. However, in large establishments whose distribution is on a national or even international scale, millions of cases of empty bottles are frequently kept on hand in warehouses. Under these circumstances, the slip sheet technique becomes extremely expensive and impractical.
One suggested solution to the problem of depalletizing has been to lift off the top layer of cases with a vacuum suction head and then to place the cases on a conveyor system. However, in addition to involving the installation of much expensive equipment and high ceiling requirements to permit operation of that equipment, vacuum-type equipment cannot be used in plants where the practice is to stack the cases in their inverted position unless provision were first made to rotate the full pallet 180.degree..
As an alternative to vacuum-type depalletizing, particularly where the cases are stacked on the pallets with their unglued sides down, it would be necessary to devise an efficient system for sliding individual cases from the pallet. Otherwise it would be necessary to raise and remove individual cases while suppoting them from below during the transfer process so that the bottles do not drop out and the cases would remain in the same inverted position as when they were stacked on the pallet when they are finally placed on the moving conveyor.
The material-handling art contains numerous examples of suggestions of apparatus for transferring containers or other large objects from one location to another, including to a conveyor, in which the item handled is rotated during the transfer process. In U.S. Pat. No. 1,943,530 for example, there is disclosed a machine which clamps a drum at both ends, turns it 90.degree., and then deposits it on a moving conveyor. Another patent (U.S. Pat. No. 2,520,252) discloses a machine which clamps a skid of paper at its top and bottom and rotates it 180.degree. to permit printing on both sides of the sheet. Still another patent (U.S. Pat. No. 3,024,929) discloses a device for emptying a box. The box, filled with objects which it is desired to dump onto a floor or table is placed on a pallet, the two are clamped together at their top and bottom, and then rotated 180.degree. to invert the box and dump its contents. The box is clamped at three points along its top edge while being inverted.
Because of the widespread practice of stacking cases of empty bottles on pallets with the unglued, bottom flaps of the cases facing downward, it will be readily apparent that, to transfer cases so stacked from a pallet without sliding the top layer would require rotation of individual cases or a layer of cases through a full 360.degree.. For this reason, it would not be possible to use the above referred to prior art proposals to unload and transfer the cases from pallets to a moving conveyor and to place them on the latter oriented in the same manner as on the pallets since none of the presently available machines is capable of rotating a case through a full 360.degree. arc or through any arc, for that matter, without dumping the empty bottles from the unglued side of the case.
Accordingly, a principal object of the present invention is to provide an apparatus for unloading a pallet stacked with similarly-shaped objects, parallelepiped-shaped in particular, and capable of depositing then on a surface similarly oriented as on the pallet.
Another object is to provide a depalletizing apparatus which is capable of automatically carrying out a sequence of steps from an initial presentation of a stacked pallet to the ultimate removal of an empty pallet.
Another object is to provide a novel apparatus and method for handling cases of glassware to transfer them safely from a stack on a pallet to a moving conveyor.
Still another object is to provide an apparatus which will transfer individual layers of cases from a stacked pallet without sliding the upper layer over the next lower succeeding layer of cases.
A further object is to provide an apparatus for unloading a pallet stacked with cases of empty bottles whereby individual layers of cases are manipulated through a full 360.degree. arc and deposited on a moving conveyor for transporation to a bottling machine or any other handling.
Still a further object is to provide an apparatus for unloading a pallet on which cases of bottles are stacked with the unglued side of the cases facing downward.
Yet another object is to provide such an apparatus which is capable of transferring individual cases or individual layers of cases from a stack to a conveyor and placing them on the conveyor in the same open-side downward position they occupied in the stack.
A further object is to provide a depalletizing apparatus in which emptied pallets are ejected from the device and collected for reuse.
These and other objects, which will be apparent to those skilled in this art, are achieved by means of the present invention, a description of which is set forth below.